Electrode assembly with fibers for a medical device

ABSTRACT

An apparatus and system are provided for employing an electrode for delivering an electrical signal to a portion of a tissue of a patient&#39;s body. The electrode includes a first surface to electrically couple to the portion of an outer layer of the tissue. The electrode also includes a plurality of fibers or longitudinal elements coupled to the outer surface. The plurality of fibers or longitudinal elements are adapted to migrate to an interior portion of the tissue.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to an apparatus for delivering anelectrical signal to a patient's body using an implantable medicaldevice (IMD) system and, more particularly, an electrode comprisingfibrous components for improved electrical contact with a targetedportion of the patient's body for delivering a stimulation signal froman IMD.

2. Description of the Related Art

Many advancements have been made in treating diseases such as epilepsy.Therapies using electrical signals for treating these diseases have beenfound to be effective. IMDs have been effectively used to delivertherapeutic stimulation to various portions of the human body (e.g., thevagus nerve) for treating these diseases. As used herein, “stimulation”or “stimulation signal” refers to the application of an electrical,mechanical, magnetic, electro-magnetic, photonic, audio and/or chemicalsignal to a target tissue in the patient's body. The signal is anexogenous signal that is distinct from the endogenous electrical,mechanical, and chemical activity (e.g., afferent and/or efferentelectrical action potentials) generated by the patient's body andenvironment. In other words, the stimulation signal (whether electrical,mechanical, magnetic, electro-magnetic, photonic, audio, or chemical innature) applied to the tissue in the present invention is a signalapplied from an artificial source, e.g., a neurostimulator.

A “therapeutic signal” refers to a stimulation signal delivered to apatient's body with the intent of treating a disorder by providing amodulating effect to the target tissue, e.g., a neural tissue. Theeffect of a stimulation signal on electrical, chemical and/or mechanicalactivity in the target tissue is termed “modulation”; however, forsimplicity, the terms “stimulating” and “modulating”, and variantsthereof, are sometimes used interchangeably herein. In general, however,the delivery of an exogenous signal itself refers to “stimulation” ofthe target tissue, while the effects of that signal, if any, on theelectrical, chemical and/or mechanical activity of the target tissue areproperly referred to as “modulation.” The modulating effect of thestimulation signal upon the target tissue may be excitatory orinhibitory, and may potentiate acute and/or long-term changes inelectrical, chemical and/or mechanical activity. For example, the“modulating” effect of the stimulation signal to a target neural tissuemay comprise one more of the following effects: (a) initiation of anaction potential (afferent and/or efferent action potentials); (b)inhibition or blocking of the conduction of action potentials, whetherendogenously or exogenously induced, including hyperpolarizing and/orcollision blocking, (c) affecting changes inneurotransmitter/neuromodulator release or uptake, and (d) changes inneuro-plasticity or neurogenesis of brain tissue.

Electrical neurostimulation may be provided by implanting an electricaldevice underneath the patient's skin and delivering an electrical signalto a nerve, such as a cranial nerve. In one embodiment, the electricalneurostimulation involves sensing or detecting a body parameter, withthe electrical signal being delivered in response to the sensed bodyparameter. This type of stimulation is generally referred to as“active,” “feedback,” or “triggered” stimulation. In another embodiment,the system may operate without sensing or detecting a body parameteronce the patient has been diagnosed with a medical condition that may betreated by neurostimulation. In this case, the system may apply a seriesof electrical pulses to the nerve (e.g., a cranial nerve such as a vagusnerve) periodically, intermittently, or continuously throughout the day,or over another predetermined time interval. This type of stimulation isgenerally referred to as “passive,” “non-feedback,” or “prophylactic,”stimulation. The electrical signal may be applied by an IMD that isimplanted within the patient's body. In another alternative embodiment,the signal may be generated by an external pulse generator outside thepatient's body, coupled by an RF or wireless link to an implantedelectrode.

Generally, neurostimulation signals that perform neuromodulation aredelivered by the IMD via one or more leads. The leads generallyterminate at their distal ends in one or more electrodes, and theelectrodes, in turn, are electrically coupled to tissue in the patient'sbody. For example, a number of electrodes may be attached to variouspoints of a nerve or other tissue inside a human body for delivery of aneurostimulation signal.

Turning now to FIG. 1, a prior art electrode 100 operatively coupled toa nerve bundle 120 comprising a plurality of individual nerve fibers oraxons, is illustrated. The electrode 100 comes into contact with theexternal periphery of the nerve 120 to deliver an electrical signal tothe nerve. The electrode 100 includes a first helical portion 112, asecond helical portion 114 and an anchor 116 that couples the electrodeto the nerve bundle 120. The first helical portion 112 may be a cathodeportion, and the second helical portion 114 may be an anode portion ofthe electrode 100. The electrode 100 is coupled to a lead that carriesan electrical signal from the IMD Typically, state-of-the-artneurostimulation electrodes deliver electrical signals to the outersurface 140 of nerve bundle 120. Generally, this disposition of thestimulation electrode 100 only provides penetration of electrical chargeinto areas near the outer surface 140 of the nerve bundle 120.Accordingly, state-of-the-art electrodes 100 may only achieve anactivation of a small percentage of the nerve axons in the nerve bundle120. Some estimates have suggested that as little as 5% of the totalpopulation of nerve axons within a nerve bundle may be activated usingstate-of-the-art electrodes 100.

State-of-the-art electrodes 100 may only provide adequate stimulation(i.e., may only modulate electrical activity of) individual nerve fibers(axons) that are in close proximity to the outside surface of the nervetrunk. Some patients may not respond to neurostimulation therapy due tothe failure of electrical signals delivered to the outer portions of thenerve trunk 120 to penetrate to a sufficient depth within the nervetrunk to recruit nerve axons that are relevant to the patient'scondition. This factor may result in a reduced efficacy of the therapyor in some cases a complete failure of the patient to respond to thetherapy.

Another problem associated with the state-of-the-art electrodes 100 isthat, as a result of the attenuation described above, a signal withlarger power than otherwise would have been required, is needed toachieve desired efficacy. Physicians may be compelled to increase thedosage, i.e., frequency, power, pulse width, etc., of stimulationsignals to achieve desired efficacy. This excessive usage of power mayresult in reduced battery life because of the portion of the electricalsignal that is non-therapeutic or sub-optimal in achieving therapeuticefficacy.

The present invention is directed to overcoming, or at least reducing,the effects of one or more of the problems set forth above.

SUMMARY OF THE INVENTION

In one aspect, an apparatus is provided for employing an electrode fordelivering an electrical signal to a target nerve of a tissue of apatient's body, wherein the nerve comprises an outer surface and aninner portion. The electrode includes an inner surface to contact to theouter surface of the target nerve. The electrode also includes aplurality of fiber elements comprising a proximal end and a distal end.The fiber elements are coupled at the proximal end to the inner surfaceof the electrode.

In another aspect, an apparatus is provided for employing an electrodefor delivering an electrical signal to a target nerve of a tissue of apatient's body, wherein the nerve comprises an outer surface and aninner portion. The electrode includes a first surface to electricallycouple to the cranial nerve. The electrode also includes a plurality offibers having a proximal end and a distal end. Each of the fibers iscoupled to the first surface at the proximal end. The fibers areconductive and adapted to migrate beneath the outer surface of thecranial nerve to deliver an electrical signal to the inner portion ofthe cranial nerve.

In yet another aspect of the present invention, an implantable medicaldevice system is provided for delivering an electrical signal to aportion of a target tissue of a patient's body. The tissue comprises anouter surface and an interior portion. The IMD system includes an IMDfor generating an electrical signal. The system also includes anelectrode that is operatively coupled to the IMD. The electrode isprovided for delivering the electrical signal to the target tissue of apatient's body. The electrode includes a first surface to electricallycouple to an outer surface of the target tissue. The electrode alsoincludes a plurality of longitudinal elements coupled to the firstsurface. The plurality of longitudinal elements are adapted toelectrically couple to at least one of the outer surface and theinterior portion of the target tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIG. 1 illustrates a prior art electrode used with implantable medicaldevices, the electrode being coupled to a nerve trunk;

FIG. 2 provides a stylized diagram of a system that includes an IMD andan electrode implanted into a patient's body for providing a therapeuticelectrical signal to a neural structure of the patient's body, inaccordance with one illustrative embodiment of the present invention;

FIG. 3 illustrates a stylized depiction of a cross-sectional depictionof a target nerve for a therapeutic electrical signal;

FIG. 4 illustrates a cross-sectional view of a nerve, including astylized isometric depiction of mylinated axon and an unmyelinated axon;

FIG. 5A illustrates an electrode coupled to a nerve, in accordance withone illustrative embodiment of the present invention;

FIG. 5B illustrates a helical configuration of the electrode, inaccordance with one illustrative embodiment of the present invention;

FIG. 6 illustrates a stylized depiction of a portion of an electrode incontact with a nerve, along with stylized, cross-sectional view of thenerve in accordance with one illustrative embodiment of the presentinvention;

FIG. 7 illustrates a stylized depiction of a fibrous material coupled toan electrode, along with a stylized, magnified depiction of the fibrousmaterial, in accordance with one illustrative embodiment of the presentinvention; and

FIG. 8 illustrates a stylized, magnified, cross-sectional depiction ofan electrode with an insulating material, in accordance with oneillustrative embodiment of the present invention.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Illustrative embodiments of the invention are described herein. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. In the development of any such actualembodiment, numerous implementation-specific decisions must be made toachieve the design-specific goals, which will vary from oneimplementation to another. It will be appreciated that such adevelopment effort, while possibly complex and time-consuming, wouldnevertheless be a routine undertaking for persons of ordinary skill inthe art having the benefit of this disclosure.

This document does not intend to distinguish between components thatdiffer in name but not function. In the following discussion and in theclaims, the terms “including” and “includes” are used in an open-endedfashion, and thus should be interpreted to mean “including, but notlimited to.” Also, the term “couple” or “couples” is intended to meaneither a direct or an indirect electrical connection. “Direct contact,”“direct attachment,” or providing a “direct coupling” indicates that asurface of a first element contacts the surface of a second element withno substantial attenuating medium there between. The presence ofsubstances, such as bodily fluids, that do not substantially attenuateelectrical connections does not vitiate direct contact. The word “or” isused in the inclusive sense (i.e., “and/or”) unless a specific use tothe contrary is explicitly stated.

The term “electrode” or “electrodes” described herein may refer to oneor more stimulation electrodes (i.e., electrodes for delivering anelectrical signal generated by an IMD to a tissue), sensing electrodes(i.e., electrodes for sensing a physiological indication of a patient'sbody), and/or electrodes that are capable of delivering a stimulationsignal, as well as performing a sensing function.

Cranial nerve stimulation has been proposed to treat a number ofdisorders pertaining to or mediated by one or more structures of thenervous system of the body, including epilepsy and other movementdisorders, depression, anxiety disorders and other neuropsychiatricdisorders, dementia, traumatic brain injury, head trauma, coma, migraineheadache, obesity, eating disorders, sleep disorders, cardiac disorders(such as congestive heart failure and atrial fibrillation),hypertension, endocrine disorders (such as diabetes and hypoglycemia)and pain, among others. See, e.g., U.S. Pats. Nos. 4,867,164; 5,299,569;5,269,303; 5,571,150; 5,215,086; 5,188,104; 5,263,480; 6,587,719;6,609,025; 5,335,657; 6,622,041; 5,916,239; 5,707,400; 5,231,988; and5,330,515. Despite the numerous disorders for which cranial nervestimulation has been proposed or suggested as a treatment option, thefact that detailed neural pathways for many (if not all) cranial nervesremain relatively unknown, makes predictions of efficacy for any givendisorder difficult or impossible. Moreover, even if such pathways wereknown, the precise stimulation parameters that would modulate particularpathways relevant to a particular disorder generally cannot bepredicted.

Despite the difficulties of predicting efficacy for particulardisorders, the use of vagus nerve stimulation as a therapy for treatingepilepsy and/or depression is an established therapy option. Electrodesmay be used in a system to deliver therapeutic electrical signals froman IMD to a target portion of a patient's body (e.g., a vagus nerve) fortreating these and other diseases. Embodiments of the present inventionprovide for a “fibrous electrode,” which refers to an electrode uponwhich one or more “fibers” may be coupled. Some embodiments of thepresent invention provide for a “longitudinal element” coupled to asurface of an electrode. As used herein, a longitudinal element refersto an element whose longest dimension substantially exceeds otherdimensions, e.g., length, width, cross-section, etc. Thus, alongitudinal element may comprise a “fiber” as previously disclosed. Anexample of a fiber may include, but is not limited to, a flexiblematerial that is in mechanical and electrical communication with theelectrode. These flexible materials may be formed from carbon nanotubesor interwoven fibers comprising carbon nanotubes, a variety ofconductive materials, a variety of semi-conductive materials, and/orother materials that are relatively thin, strong and electricallyconductive, or combinations of the foregoing. Embodiments of the presentinvention provide for an electrode that comprises one or more fibersthat may be capable of penetrating an outer surface of a target tissue(e.g., a nerve bundle or an individual nerve) upon which the electrodeis operatively coupled. Where the target tissue is a nerve bundle, thefibers of the electrode may penetrate the outer surface of a portion ofthe nerve to reach an interior portion of the nerve bundle to allow anelectrical signal to be applied within the nerve bundle. Such anelectrode will advantageously allow for greater electrical flux into thetarget nerve, and may permit recruitment and/or modulation of nervefibers not capable of modulation with prior art electrodes coupled onlyto an outer surface of the nerve. Embodiments of the present inventionprovide for a fibrous neurostimulation electrode that is capable ofdelivering electrical signals to an interior portion of a cranial nerve.

Utilizing embodiments of the present invention, the penetration of thefibrous material operatively coupled to the electrode into the interiorportion of the nerve may be used to cause the electrical signal topenetrate into the interior portions of the tissue to a greater depththan electrodes lacking said fibrous material, e.g., to various nervefibers (axons) within the nerve bundle. Therefore, utilizing theelectrodes of embodiments of the present invention, an increasedpopulation of nerve fibers may be modulated by the electrical signal.The “fibrous” or “fiber” electrodes of the present invention providesfor conductive communication with an interior portion of the nerve. Thefiber or fibrous material may be of one or more of a plurality ofmaterials, such as a stainless steel fiber, a carbon nanotube fiber, aconductive graphite fiber, a titanium fiber, a gold fiber, a copperfiber, silicon oxide, and/or one or more of any of a plurality ofconductive materials capable of being formed into fibers of relativelysmall dimensions, e.g., below 1.0 mm.

The fibrous electrodes disclosed by embodiments of the present inventionmay also be used for sensing operations. Therefore, the fibers e.g.,microfibers or nanofibers, that are coupled to a first electrode mayprovide for an increased population of nerve fibers being included andobserved in sensing operations. Further, utilizing embodiments of thepresent invention, a decreased amount of current density may be requiredto modulate a larger number of nerve fibers. This may provide for usageof a lower power stimulation signal, while achieving equal or betterdelivery of therapeutic signals, and/or may allow therapeutic efficacyto be achieved for patients who otherwise would not respond to theelectrical signal therapy.

Embodiments of the present invention provide for applying apredetermined amount of force upon the fibrous electrode, which mayprompt the fibers coupled to the electrode to migrate into the nervebundle in a relatively slow manner. In this manner, penetration of thenerve bundles may be achieved over time without substantially causingexcessive trauma to the nerve or surrounding tissue. Further, amultiplexing scheme may be used to deliver current or electrical signalsto various portions of a nerve in a predetermined sequence. For example,during a first time period, the electrical signal may be applied to anexterior surface of the nerve using a first surface of the electrode,while during a second time period, the electrical signal may be appliedto an interior portion of the nerve using a second, fibrous portion ofthe electrode. In this manner, a multiplexing scheme may be used toprompt increased diversity of nerve fibers recruited by the electricalsignal. Similar benefits may be obtained when the electrode is used tosense electrical activity in the nerve bundle.

Although not so limited, a system capable of implementing embodiments ofthe present invention is described below. FIG. 2 depicts a stylizedimplantable medical system 200 for implementing one or more embodimentsof the present invention. An electrical signal generator 210 isprovided, having a main body 212 comprising a case or shell with aheader 216 for connecting to an insulated, electrically conductive leadassembly 222. The generator 210 is implanted in the patient's chest in apocket or cavity formed by the implanting surgeon just below the skin(indicated by a dotted line 245, similar to the implantation procedurefor a pacemaker pulse generator.

A fibrous electrode assembly 225, preferably comprising a plurality ofelectrodes having at least an electrode pair, is conductively connectedto the distal end of the lead assembly 222, which preferably comprises aplurality of lead wires (one wire for each electrode). Each electrode inthe electrode assembly 225 may operate independently or alternatively,may operate in conjunction with the other electrodes. Each electrode maycomprise one or more fibrous electrodes for applying electrical signalsto a nerve bundle. In some embodiments, the fibrous portions of theelectrode penetrate an outer surface of the nerve bundle to deliverelectrical charge to an interior of the nerve bundle. In otherembodiments, the fibers do not penetrate into the interior of the nerve,but provide for a higher charge flux into the target portion of thenerve compared to prior art electrodes. Some prior art electrodes forstimulation of neural tissues have extremely small surface areas,resulting in relatively high electrical flux across that area. When theelectrical flux exceeds a threshold, the molecules of the metalelectrode can be dissolved into the surrounding body fluids, which isusually toxic to the neural tissue. Because the fibers coupled to theelectrode significantly increase the surface area across which theelectrical charge is transferred, it provides a significantly reducedrisk of electrode dissolution, thereby providing increased safety wherea patient is treated with relatively strong electrical signals.

Referring again to FIG. 2, lead assembly 222 is attached at its proximalend to connectors on the header 216 of generator 210. The electrodeassembly 225 may be surgically coupled to a vagus nerve 227 in thepatient's neck or at another location, e.g., near the patient'sdiaphragm or at the esophagus/stomach junction. Other (or additional)cranial nerves, such as the trigeminal and/or glossalpharangeal nervesmay also be used to deliver the electrical signal in particularalternative embodiments. In one embodiment, the electrode assembly 225comprises a bipolar stimulating electrode pair 226, 228. Suitableelectrode assemblies which could be modified to provide embodiments ofthe present invention are available from Cyberonics, Inc., Houston,Tex., USA as the Model 302 electrode assembly. However, persons of skillin the art will appreciate that many prior art electrode designs couldbe modified to provide embodiments of the present invention. Moreover,other electrodes, such as spinal cord electrodes, deep brain stimulation(DBS) electrodes, electrodes for muscle stimulation, and electrodes forstimulation of organs or even bones could also be modified to provideembodiments of the present invention. In one embodiment, the twoelectrodes are wrapped about the vagus nerve, and the electrode assembly225 may be secured to the nerve 227 by a spiral anchoring tether 230,such as that disclosed in U.S. Pat. No. 4,979,511 issued Dec. 25, 2990to Reese S. Terry, Jr., and assigned to the same assignee as the instantapplication. Lead assembly 222 is secured, while retaining the abilityto flex with movement of the chest and neck, by a suture connection tonearby tissue (not shown). While the electrode assembly 225 in FIG. 2 isdescribed in terms of a stimulating electrode, it will be appreciatedthat in alternative embodiments, the electrode assembly 225 may comprisea sensing electrode for sensing, e.g., heart rate, electrical activityin the target nerve, temperature, or other body parameters.

The electrical pulse generator 210 may be programmed with an externaldevice, such as computer 250 using programming software known in the artof implantable medical devices. A programming wand 255 may be coupled tothe computer 250 as part of the external device to facilitate radiofrequency (RF) communication between the computer 250 and the pulsegenerator 210. The programming wand 255 and computer 250 permitnon-invasive communication with the generator 210 after the latter isimplanted. In systems where the computer 250 uses one or more channelsin the Medical Implant Communications Service (MICS) bandwidths, theprogramming wand 255 may be omitted to permit more convenientcommunication directly between the computer 250 and the pulse generator210.

Turning now to FIG. 3, a cross-sectional stylized view of a nerve or anerve bundle 300 is illustrated. The nerve or nerve bundle 300 maycomprise an outer surface 340 and an inner portion 350 comprising aplurality of axons 310 and connective tissue 320. The axons 310transport electrical action potentials along the axis of the nerve 300.Typically, one or more axons 310 affecting the patient's medicalcondition may not be sufficiently stimulated using state-of-the-artelectrodes that deliver electrical signals to the exterior surface ofthe nerve bundle 300. Embodiments of the present invention provide formore robust stimulation since internal portions of the nerve may be moredirectly stimulated, and/or lower electrical flux values across theelectrode providing increased safety.

Referring to FIG. 4, a cross-sectional view of the nerve bundle 300 witha stylized, isometric depiction of a myelin nerve sheath 410 surroundingan axon 310 is illustrated. It is known in the art that large nervebundles, such as the vagus nerve, include multiple nerve types nerves,such as A and B fibers, which are large-diameter fibers having a myelinsheath such as sheath 410, and C fibers, which are small-diameter fiberslacking a myelin coating. These major fiber types also have numeroussub-types. The A and B fibers typically conduct action potentials atmuch faster speeds along the nerve than C fibers, and have a lowerthreshold for the induction of action potentials with an appliedelectric signal. Typically, the electric signal applied to the exteriorof the nerve bundle 300 may at least partially attenuate as it travelsradially from the outer surface 340 of the nerve 300 to interior portion350 and towards the central axis. Accordingly, axons of a given typenear the outer surface 340 are more likely to receive sufficientelectrical charge to induce an action potential than are axons in theinterior portion of the nerve 300, with the likelihood of a givenelectrical charge inducing an action potential in an individual axondecreasing radially from the outer surface 340 to the central axis ofthe nerve. Embodiments of the present invention provide for fibrouselectrodes that may penetrate the surface of the nerve 300 and/or thenerve sheath 410 to enhance delivery of electrical charge to axons nearthe center of the nerve 300. In this manner, a greater percentage ofvarious nerve fibers within the nerve bundle 300, such as the A fibers,the B fibers and/or the C fibers may be targeted and stimulatedsufficiently to induce action potentials, as compared to prior artelectrodes.

Referring simultaneously to FIGS. 5A and 5B, an electrode comprisingfibers and/or spikes on its inner surface, capable of being engaged to atissue (e.g., a nerve bundle 300) of a human body, is provided. FIG. 5Aillustrates an electrode 500 in contact with a nerve bundle 300, inaccordance with one illustrative embodiment of the present invention.FIG. 5B illustrates a helical electrode, wherein an inner surface 540 ofthe electrode 500 comprises a plurality of fibers and/or spikes 550coupled thereto. Nerve bundle 300 is generally cylindrical and comprisesa central axis. The electrode 500 of FIG. 5A may comprise a plurality offiber elements 550 that are coupled to the electrode 500. The fibers 550may refer to a plurality of materials that are conductive and suitablefor joining to an inner surface 540 of the electrode 500. Inner surface540 is suitable for engaging outer surface 340 of the nerve bundle 300,while fibers 550 may engage either outer surface 340 or an inner portion350 of the nerve bundle 300. The fibers 550 may deliver the electricalsignals directly to any portion of the nerve 300 with which in comesinto contact. In one embodiment, the electrode 500 is a helical shapedapparatus (as depicted in FIG. 5B) that may be wrapped about the nervebundle 300. FIG. 5B also illustrates an end member 545 that provides aninterface to a lead wire in electrical communication with the IMD. Inone embodiment, the electrode 500 comprises at least a firstcircumneural cathode portion 560 and a second circumneural anode portion570. The first circumneural portion 560 and/or the second circumneuralportion 570 comprise a plurality of fibers 500 described herein forcontacting a portion of the target nerve bundle 300.

FIG. 5A also illustrates a stylized magnification of a portion of theelectrode 500. In the circumneural electrode 500, each element 560, 570may comprise a number of fibers 550 that protrude outward from the innersurface 540 of the electrode 500 and/or from the side surfaces 543 ofthe electrode 500 at one or more angles relative to the inner surface540 or the side surfaces 543. In one embodiment, the fibers 550 in theinner surface 540 of the electrode may protrude radially inwardly fromthe inner surface 540 of the elements 560, 570 toward the axis of thenerve bundle 300 (as exemplified in FIGS. 5A and 5B). The fibers 550 maybe coupled to the electrode 500 in a number of ways, includingsoldering, micro-welding, using adhesives, photolithography process,and/or various manufacturing techniques, etc. The fibers 550 may be of aflexible configuration, a medium rigid configuration, and/or of a rigidconfiguration (e.g., a spike). They may also be, in some embodiments, ofnon-uniform cross-section, e.g., thicker at the proximal end andnarrowing at the distal end. The fiber 550 may be a longitudinalelement, which may refer to an element whose longest dimensionsubstantially exceeds other dimensions, e.g., length, width,cross-section, etc. Thus, a longitudinal element may comprise a “fiber”as previously disclosed.

The fibers 550 provide for an electrical path from the IMD 200, throughthe lead assembly 222, through the electrode 500, and onto an innerportion of a nerve bundle 300. More specifically, the electrode 500provides a path from the fibers 550 and inner surface 540 of the cathodeelement 560, through the outer surface 340 of the nerve and into theinner portion 350 thereof, through the nerve tissue and into the fibers550 and inner surface 540 of the anode element 570.

Turning now to FIG. 6, a stylized depiction is provided of a portion ofan element (560, 570) of the electrode 500 in contact with a nervebundle 300. FIG. 6 also depicts a stylized, cross-sectional view of thenerve bundle 300, in accordance with one embodiment of the presentinvention. The electrode 500 may comprise an inner surface 540 andnumber of fibers 550. For clarity of illustration inner surface 540 isshown in only partial contact with outer surface 340 of nerve 300.However, in an actual embodiment, substantially all of inner surface 540would engage outer surface 340 of nerve 300. The fibers 550 may engageeither outer surface 340 or inner portion 350 of nerve 300. The fibersmay penetrate, through migration, the surface of the nerve 300 over aperiod of time (e.g., many days, weeks, etc.). In one embodiment,external force may be applied to prompt the migration of the fibers 550into the nerve bundle 300. In an alternative embodiment, the electrode500 may be positioned around the nerve 300 in a manner, such thatwithout applying external force, the fibers 550 may penetrate thesurface of the nerve bundle 300. In one such embodiment, electrodeelements 560, 570 may comprise a resilient material, such as a siliconepolymer or other known biocompatible materials. The electrode elementsmay be formed to provide a slight constrictive resilient force on nerve300 to maintain contact between the electrode element (560, 570) and thenerve 300, and to assist fibers 550 to penetrate into the inner portion350 of nerve bundle 300.

In one embodiment, the penetration of the fibers 550 into the nerve 300may take place at such a rate that trauma to the nerve 300 iseliminated. In yet another alternative embodiment, migration of thefibers 550 may be controlled by electrical means (e.g., by providingpredetermined electrical pulses to prompt migration of the fibers 550)such that the fibers 550 may penetrate the outer surface 340 of thenerve 300 substantially without causing excessive damage to the nerve.Other means, such as external force, small movement, etc., may be usedto cause the penetration of the fibers into the neurons. In stillanother embodiment, fibers 550 may be formed of a shape-memory metalsuch as Nitinol, and coupled by known means substantially perpendicularto inner surfaces 540 of an electrode element. The fibers may then besubstantially flattened against inner surface 540 by mechanical means,thereby rendering the electrode element easier and safer to couple tothe nerve. The shape-memory metal may be fabricated to return to itsfabrication state (i.e., substantially perpendicular to inner surface540) at a predetermined temperature, e.g., a temperature at or slightlyabove or below body temperature. Thus, after the electrode 500 iswrapped around the nerve 300, the temperature of the patient's bodycauses the fibers 550 to return to a substantially perpendicularorientation relative to inner surface 540 to facilitate penetration ofthe fibers 550 into inner portion 350 of the nerve 300.

FIG. 6 further illustrates that, in some cases, some fibers 550 of theelectrode 500 may penetrate various portions of the nerve bundle 300. Byproviding fibers of differing lengths, nerve fibers at various radialdistances from the outer surface 340 may be selectively targeted forstimulation.

FIG. 7 illustrates a stylized, magnified depiction of one embodiment ofa fiber 550 of an electrode 500, in accordance with one illustrativeembodiment of the present invention. In some embodiments of the presentinvention, the fiber 550 may comprise a fiber insulation 710 and aconductive portion 720. A segment of the conductive portion 720 may beencapsulated by a fiber insulation 710 such that only the exposedportion of the fiber 550 (i.e., the conductive portion 720) is capableof delivering a stimulation signal. In this manner, penetration toparticular radial depths within the nerve 300 may be achieved. Forexample, referring simultaneously to FIGS. 6 and 7, a fiber 550 thatpenetrates the surface of the nerve bundle 300 and moves intosignificant proximity of the axons 310 may have an exposed conductiveportion 720 that comes into contact with the axons 310. In other words,the remaining portion of the fiber 550 (i.e., the portion from the innersurface 540 of the electrode through the nerve bundle 300, and to adesired depth within interior portion 350 of the nerve bundle) isinsulated and only the tip of the nerve of the fiber 550 is exposed.Thus, only the axons 310 in the immediate vicinity of the conductionportion 720 of the fiber 550 will be stimulated. Therefore, a specifictargeting and/or more effective stimulation, of A-fibers, B-fibers,C-fibers and/or the axons 310 in the interior portion 350 of the nerve300 may be achieved by insulating portions of the fiber 550 and exposingonly the conductive portion 720 to target more specific regions of thenerve bundle 300.

In alternative embodiments substantially the entire length of the fibers550 may be conductive, and penetration of charge into specific areas ofthe inner portion 350 of the nerve 300 may be controlled by thedistribution and length of the fibers 550.

FIG. 8, illustrates a stylized, magnified, cross-sectional depiction ofa portion of the electrode 500 and associated fibers 550, in accordancewith an illustrative embodiment of the present invention. In thisembodiment of the present invention, the inner surface 540 of electrode500 may be coated with an insulating material (electrode insulation810), similar to the insulation 710 on portions of the fibers 550,discussed above with respect to FIG. 7. In this configuration, neitherthe inner surface 540 of electrode 500 nor the insulated portions of thefiber 550 provide electrical stimulation to the nerve. Instead, only theconductive portion 720 (i.e., the exposed tip) of the fiber 550 deliversthe electrical signal to the nerve 330. Therefore, a more focuseddelivery of the stimulation signal may be provided to the interior 350of the nerve 300, as opposed to the exterior 340. Thus, portions of thenerve bundle 300 may be specifically targeted without providingstimulation to other portions of a nerve bundle 300. In this manner,focused delivery of stimulation to specific portions of a nerve bundle300 may be achieved. Utilizing multi-plexing of delivery of theelectrical signal, a sequence of targeted electrical signals throughouta nerve bundle 300 may be achieved for increased efficacy and targeteddelivery of stimulation signals.

Utilizing embodiments of the present invention, a more robust deliveryof electrical signal/stimulation may be achieved. This may increaseefficacy and provide various advantages, such as increased population ofnerve fibers being activated by stimulation. Further advantages providedby embodiments of the present invention may include increased populationof nerve fibers being accessed for observation during sensingoperations. These advantages may lead to a reduction of the power usedby the IMD since more direct current electrical signals may be provided.

All of the methods and apparatuses disclosed and claimed herein may bemade and executed without undue experimentation in light of the presentdisclosure. While the methods and apparatus of this invention have beendescribed in terms of particular embodiments, it will be apparent tothose skilled in the art that variations may be applied to the methodsand apparatus and in the steps, or in the sequence of steps, of themethods described herein without departing from the concept, spirit, andscope of the invention, as defined by the appended claims. It should beespecially apparent that the principles of the invention may be appliedto selected cranial nerves other than, or in addition to, the vagusnerve to achieve particular results in treating patients havingepilepsy. More generally, the techniques and apparatus of the presentinvention may be applied to any neural structure with regard to which amore controlled delivery of an electrical signal throughout thestructure (as opposed to its periphery only) is desired or needed.

The particular embodiments disclosed above are illustrative only as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown other than as describedin the claims below. It is, therefore, evident that the particularembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope and spirit of the invention.Accordingly, the protection sought herein is as set forth in the claimsbelow.

1. An electrode for delivering an electrical signal to a target nerve ofa patient's body, wherein said nerve comprises an outer surface and aninner portion, said electrode comprising: an inner surface to contact tosaid outer surface of said target nerve; and a plurality of fiberelements comprising a proximal end and a distal end, wherein said fiberelements are coupled at said proximal end to said inner surface of saidelectrode.
 2. The electrode of claim 1, wherein said plurality of fiberelements are adapted to migrate into said inner portion of said targetnerve.
 3. The electrode of claim 1, wherein said fiber elements arecomprised of at least one conductive material selected from the groupconsisting of copper, titanium, an alloy metal, iron, steel, and acarbon-based structure.
 4. The electrode of claim 3, wherein each ofsaid fiber elements comprises an electrically insulated portionproximate to said proximal end and a conductive portion proximal to saiddistal end.
 5. The electrode of claim 1, wherein said target nerve is acranial nerve selected from the group consisting of a vagus nerve, aglossopharyngeal nerve, and a trigeminal nerve, and said fiber elementsare capable of penetrating said outer surface of said target nerve. 6.The electrode of claim 1, wherein said fiber elements are comprise avariety of lengths adapted to penetrate a plurality of distances intosaid target nerve.
 7. The electrode of claim 6, wherein said innersurface of said electrode is substantially nonconductive, and wherein afirst portion of said fiber elements is encapsulated with anelectrically insulating material, electrically exposing a conductivesecond portion of said fiber element to said target nerve.
 8. Theelectrode of claim 1, wherein said electrode is a circumneural electrodesuch that said first surface substantially surrounds said outer surfaceof said target nerve.
 9. The electrode of claim 1, wherein saidelectrode further comprises an electrical signal to apply to said targetnerve to treat at least one of depression disorder and an epilepsydisorder.
 10. The electrode of claim 1, wherein said electrode furthercomprises: a circumneural cathode that surrounds a first portion of saidtarget nerve, said circumneural cathode comprising a first plurality offiber elements capable of migrating into said inner portion of saidtarget nerve; and a circumneural anode that surrounds a second portionof said target nerve, said circumneural anode comprising a secondplurality of fiber elements capable of migrating into said inner portionof said target nerve.
 11. An electrode for delivering an electricalsignal to a portion of a cranial nerve of a patient's body, said cranialnerve having an outer surface and an inner portion, said electrodecomprising: a first surface to electrically couple to said cranialnerve; and a plurality of fibers having a proximal end and a distal end,wherein each of said fibers is coupled to said first surface at saidproximal end, said fibers being conductive and adapted to migratebeneath the outer surface of the cranial nerve to deliver an electricalsignal to said inner portion of said cranial nerve.
 12. The electrode ofclaim 11, wherein said first surface is a helical structure adapted tobe wrapped around said cranial nerve.
 13. The electrode of claim 11,wherein said fibers are oriented generally perpendicular to said firstsurface of said electrode.
 14. The electrode of claim 11, wherein saidplurality of fibers are comprised of at least one conductive materialselected from the group consisting of copper, titanium, an alloy metal,iron, steel, a shape memory metal and a carbon nanotube structure. 15.The electrode of claim 14, wherein said plurality of fibers arecomprised of a shape-memory metal capable of returning to a desiredorientation upon reaching a threshold temperature.
 16. An implantablemedical device system for providing an electrical signal therapy to apatient, comprising: an implantable medical device for generating anelectrical signal; and an electrode operatively coupled to saidimplantable medical device for delivering said electrical signal to aportion of a target tissue of a patient's body, said target tissuecomprising an outer surface and an interior portion, said electrodecomprising: a first surface that electrically couples to said outersurface of said target tissue; and a plurality of longitudinal elementscoupled to said first surface, said longitudinal elements being adaptedto electrically couple to at least one of said outer surface and saidinterior portion of said target tissue.
 17. The implantable medicaldevice system of claim 16, further comprising a lead assembly, said leadassembly comprising a proximal portion adapted to be connected to theimplantable medical device and a distal portion being adapted to becoupled to said electrode, said lead assembly to carry said electricalsignal from said implantable medical device to said electrode.
 18. Theimplantable medical device system of claim 16, wherein said longitudinalelements comprise fiber elements capable of migrating within saidinterior portion of said target tissue.
 19. The implantable medicaldevice system of claim 18, wherein said fiber elements is comprised ofat least one conductive material selected from the group consisting ofcopper, titanium, an alloy metal, iron, steel, a shape memory metal, anda carbon-based structure.
 20. The implantable medical device system ofclaim 18, wherein said longitudinal elements comprises an electricallyinsulated portion proximate to said firs surface of the electrode and aconductive portion distal to said first surface.